Photoconductive targets



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N. C. ANDERSON PHOTOCONDUCTIVE TARGETS Filed April 5, 1951 m mmnm m m rum to QQ'QQ '09] N NNNNNNNQ "I H H 'I H W H H //V VEN TOR N.6.ANDER$ON B flaw/a4 ATTORNEY United States Patent PHOTOCONDUCTIVE TARGETS Norman C. Anderson, Auburndale, Mass., assignor to Electronics Corporation of America, a corporation of Massachusetts Application April 5, 1951, Serial No. 224,707

4 Claims. (Cl. 20163) This invention relates to photoelectric target arrangements for translating each of a plurality of specified positions and/or shapes of an impinging light beam into a unique electrical output.

The principal object of this invention is to greatly simplify photoelectric target structures which are used for generating a unique electrical output in response to the particular positioning and/or cross-sectional shape of.

an impinging light beam.

Another object is to greatly reduce the size of photoelectric target structures whereby corresponding reductions can be made in the size of the associated apparatus.

Another object is to provide a photoelectric target structure which is compact, mechanically reliable, and relatively easy and economical to manufacture.

Photoelectric target structures comprising a bank of photoelectric cells have been used in the prior art in many different types of information systems. In one system, the information to be transmitted or utilized is repre sented by the various hole or non-hole combinations of punched cards. One or more of these punched cards is located between a light source and a photoelectric target structure so that only the exposed cells of the target are subjected to light. These cells respond in the characteristic photoelectric manner to produce an electric output which is determined by the punched combination of the cards and which can be utilized to provide a variety of functions.

In another type of information system, the light from a source is shaped to assume a cross-sectional area identical to that Of an alphabetical or numerical character. This light impinges upon a photoelectric target so that the output thereof can be used, for example, to reproduce the input character at a distant point in an enlarged manner. The outlines of pictures have also been reproduced by similar arrangements in which the output of a photoelectric target is transmitted to a bank of lamps closely spaced with respect to one another so as to form a display sign or the like.

The target structures of all of these arrangements comprise a group of photoelectric cells, the number of which is usually specified by the information requirements of the system which is to use the target. Inasmuch as each of the cells heretofore utilized have comprised the conventional hermetically sealed envelope, the resulting target structure, in most instances, was larger than an optimum size. For example, a target of approximately six feet square is common for proper definition in systems reproducing the outlines of pictures. Likewise, the size of the targets in many punched card systems often requires the use of objectionably large cards so that the target structures will be covered.

Accordingly, a preferred embodiment of the photoelectric target of this invention contemplates a relatively small sized plate of insulating material having a thickness of the order of ordinary window glass. A plurality of photoconductive areas are applied directly to one or V 10, whereas grid elements A are, in a practical sense, iso-. lated from one another. Electrical connections are made ICC both of the flat surfaces of this plate. The number and the relative disposition of these areas are determined by the particular requirements of the information system which is to use a given target. In general, however, the operative functions heretofore provided by a photoelectric cell requiring considerable target surface area, as well as depth, can 'be provided by a very small area of photoconductive material of paper-like thickness applied to a relatively small surface area of this plate. A plurality of these photoconductive areas can be arranged on the plate surface so as to accomplish all of the functions of the prior art photoelectric targets with a number of distinct advantages which will be obvious from the following description.

In order that all of the features of this invention and the mode of operation thereof may be readily understood, a detailed description is set forth hereinafter, with particular reference being made to the drawings, where- 1n:

Fig. l is a perspective view of a first embodiment of this invention which can be utilized, generally speaking, for producing a unique electrical output responsive to the particular positioning of a light spot on one of a plurality of parallel lines;

Fig. 2 is a perspective view of a second embodiment of this invention which can be utilized, generally speaking, for producing a unique electrical output responsive to the particular positioning of a light spot on one of a plurality of coordinate points; and

Fig. 3 is a perspective view of a third embodiment of this invention which can be utilized, generally speaking, for also producing a unique electrical output responsive to the particular positioning of a light spot on one of a plurality of coordinate points.

The photoelectric target of the preferred embodiment shown in Fig. 1 comprises a plate-like body structure 11. The length and the Width of this plate is determined for the most part by the number, size and disposition of the photoconductive cell sections to be applied to the surface of the plate, whereas the thickness of plate 11, in general, is determined -by the mechanical durability required tivity and objectionable partial shorting of the photosensitive areas of the target.

In the initial construction of the cell, a thin coat of photoconductive material 12 is applied directly to one of the square sides of plate 11 so as to cover the entire surface thereof. This material can be of any of the types heretofore used in photoconductive cells and can be deposited and activated by processes which are well known in the art. it is preferable, however, that a material having a relatively low impedance value per unit area, such as lead sulfide, be used, so as to keep the out-' put impedance of the individual photoconductive cell sections to a value sufficiently low for direct coupling into conventional amplifiers.

Photoconductive material 12 is subdivided into a plurality of individual cell sections 1 to 9. Each of these cell sections comprises a grid element A and a grid line B arranged in a closely spaced parallel relationship with respect to one another. nected in multiple with respect to one another by electrode All of grid elements B are conto grid elements B by contact with electrode 10, and electrical connections are made to grid elements A by contact with the individual tab electrodes located on the left edge of plate 11. Grid elements A and their tab electrodes and grid elements B and their interconnecting electrode 1%) can he of graphite applied directly to the surface of photoconductive material 12 bya lead pencil, or the resulting solid deposited from anaqueous colloidal suspension, such as aquadag. It should be understood, however, thatthe grid elements and the electrodes may be of other suitable conducting materials which lend themselves to application in relatively thin adhering coats.

The individual cell sections are isolated from one another by insulating sections .C from which the photoconductive coating 12 has been removed. These insulating sections are preferably constructed by removing the appropriate portions of photoconductive material 12 by a sharp pointed instrument such as a scriber.

The vertical scale of the target structure .of Fig. l, as well as the scale of the other target structures, is greatly enlarged over the smallest possible practical size. For example, a completely workable target having approximately sixty cell sections per inch has been constructed utilizing the type of cell section shown in Fig. 1. In this arrangement each of the grid elements A and B, and the interconnecting portion of photoconductive material 12 had a surface width of approximately 0.015 inch, and each of the insulating sections L had a surface width of approximatel 0.,0linch. The length of each of these sections, as measured horizontally in the drawing, is not critical and may be of practically any size.

The entire surface of plate 11 to which the cell sections are applied is preferably hermetically sealed from the effects of water vapor and other oxidation fluids by a compound covering (notshown) so that the cell characteristics will 'be maintained for a relatively long period of time. The material used for the cover should readily transmit the wave lengths of radiant energy to which photoconductive material 12 is responsive. A compound manufactured by the General Electric Company and sold as Silicone Compound, No. 9980, is satisfactory for use with most photoconductive materials.

The active area of each of the cell sections is the long and narrow portion of photoconductive material 12 located between a grid element A and its associated grid element B. If radiations of the appropriate wave lengths impinge upon this active portion, the electrical impedance as measured between electrode and the tab electrode of the appropriate grid element A will vary in the characteristic photoconductive manner. Inasmuch as the target structure of Fig. 1 comprises nine isolated cell sections, each having a long and narrow active area and being disposed in parallel with respect to one another, this target structure can be utilized for producing nine unique electrical outputs depending upon the particular vertical positioning of an impinging light beam.

"If the intensity of each of a plurality of impinging light beams has a specified value, the target structure of Fig. 1 can also .be utilized to determine the number of light beams impinging upon a particular cell section. That is, the amplitude :of the impedance variation of that cell section will vary in defined values which can be easily translated by appropriate electrical circuits into data giving the number of impinging light beams.

The target structure of Fig. 2 utilizes the basic cell sections of Fig. l on both the front and back surfaces of plate 37 so that a unique electrical output is provided which is responsive to both the vertical and horizontal positioning of "an impinging light beam, whereas the target structure of Fig. l was responsive only to the Vertical positioning of an impinging light beam. Horizontal cell sections 21 to 28 are located on the front surface of 'plate 37. Each .of these cell sections comprises a ,grid

element ,D connected to a tab electrode on the left edge of plate 37 and .a grid element E connected to a common electrode 35 on the right edge of plate 37. The sets of grid elements are interconnected by photoconductive material 38 so as to provide complete cell sections. The adjacent cell sections are separated in the embodiment shown in the drawing by insulating sections made of a relatively wide area of the plate which is not covered by photoconductive material 38. This is to make possible the unattenuated .transmissionof.animpinging light beam to the vertical cell sections 29 to 34 located on the back side of plate 37. A preferred arrangement, however, would be to completely pack the front and back'surfaces of plate 37 with horizontally and vertically disposedcell sections. If, for example, lead sulfide of approximately 1 micron thickness is utilized for photoconductive material 33, an adequate response will be produced from the cell sections on the back surface notwithstanding the fact that the impinging radiant energy must first pass through the material on the front surface. Inasmuch as each cell section can be constructed with a width of approximately 0.060 inch, it is possible to have approxi mately 3660 responsive coordinate points to the square inch.

Each of the vertical cell sections comprises a grid element F connected to a tab electrode on the upper edge of plate 37 and a grid element G connected to a common electrode 36 on 'the bottom edge of plate37. 'The sets of vertical grid elements are interconnected by photoconductive material 39 so as to provide complete cell sections. For the reasons .hereinbefore outlined, it is also preferable that both surfaces of the target structure of Fig. 2 be hermetically sealed from oxidizing vapor'by a compound covering.

If a light beam impinges upon the intersection of two cell sections, a unique output will be generated because of the coordinate arrangement "of the sections. For example, light beam X will actuate cell sections 24 and 32 in the characteristic photoconductive manner. It is not possible for this particular combination to be actuated in response to any other coordinate positioning of an impinging light beam.

The target structure of Fig. 3 is designed to give greater target definition than the structure of Fig. 1 in arrangements wherein it is desirable to utilize only the front surface of a plate for the application of photoconductive cell section. In the initial construction of the target a plurality of metallic pins 41 are mechanically bonded to plate 40 so that they project therethrough and the top of each of the pins is exposed slightly with respect to the front surface of plate 40. Thereafter, a coat of photoconduotive material 42 is applied to the entire front surface of plate 40. This photoconductive material is subdivided into a plurality of cell sections by applying grid elements H and scribing insulating sections I in the photoconductive coat. Short vertical insulating sections J are thereafter scribed in photoconductive coat 42 so as to create small rectangular cell sections. A compound covering is also preferably applied to the entire active side of the target structure for the reasons outlined previously.

The-connections to eachofthese cell sections is made at the tab electrode for the appropriate grid element H and the appropriate pin 41. Inasmuch as the target structure of Fig. 3 comprises a plurality of small, closely spaced sections, it is possible to get sufficient definition from the target to satisfactorily reproduce the outlines of numerical and alphabetical characters, or even pictures.

It is to be understood that the above-described arrangements are illustrative of the applications of the principles of this invention. Numerous-other arrangements may be devised by those skilled in the art without departing from the scope of this invention.

What is claimed is:

1. A photoconductive target comprising a plate-like body structure of electrical insulating material, and a photoconductive coating applied directly to a surface of said body structure, said photoconductive coating being separated into photoconductive cell sections by insulating sections having no photoconductive coating, each of said cell sections including a pair of closely spaced grid elements in a parallel relationship with respect to one another and being interconnected by a relatively long and narrow layer of said photoconductive material adhering directly to said body surface.

2. A photoconductive target comprising a plate-like body structure of electrical insulating material, a photoconductive coating applied directly to a surface of said body structure, said photoconductive coating being separated into photoconductive cell sections by insulating sections having no photoconductive coating, each of said cell sections including a pair of closely spaced grid elements in a parallel relationship with respect to one another and being interconnected by a relatively long and narrow layer of said photoconductive material adhering directly to said body surface, and an electrode interconnecting one of the grid elements of each of said cell sections.

3. A photoconductive target comprising a light-transmitting plate-like body structure having two relatively large fiat surfaces, a first photoconductive coating applied directly to one of said fiat surfaces, said first photoconductive coating being separated into a first set of photoconductive cell sections by insulating sections having no photoconductive coating, each of said cell sections including a pair of closely spaced grid elements in a parallel relationship with respect to one another and being interconnected by a relatively long and narrow layer of said first photoconductive coating adhering directly to said one body surface, and a second photoconductive coating applied directly to the second of said flat surfaces, said second photoconductive coating being separated into a second set of photoconductive cell sections at right angles to said first set of cell sections by insulating sections having no photoconductive coating, each of the cell sections of the second set including a pair of closely spaced grid elements in a parallel relationship with respect to one another and being interconnected by a relatively long and narrow layer of said second photoconductive coating adhering directly to the second of said body surfaces.

4. A photoconductive target comprising a light-transmitting plate-like body structure having two relatively large flat surfaces, a first photoconductive coating applied directly to one of said fiat surfaces, said first photoconductive coating being separated into a first set of photoconductive cell sections by insulating sections having no photoconductive coating, each of said cell sections including a pair of closely spaced grid elements in a parallel relationship with respect to one another and being interconnected by a relatively long and narrow layer of said first photoconductive coating adhering directly to said one body surface, an electrode interconnecting one of the grid elements of each of said cell sections, a second photoconductive coating applied directly to the second of said flat surfaces, said second photoconductive coating being separated into a second set of photoconductive cell sections at right angles to said first set of cell sections by insulating sections having no photoconductive coating, each of the cell sections of the second set including a pair of closely spaced grid elements in a parallel relationship with respect to one another and being interconnected by a relatively long and narrow layer of said second photoconductive coating adhering directly to said second body surface, and a second electrode interconnecting one of the grid elements of each of said second set of cell sections.

References Cited in the file of this patent UNITED STATES PATENTS 919,078 Ribbe Apr. 20, 1909 1,728,073 Neale Sept. 10, 1929 2,000,379 Deisch May. 7, 1935 2,236,172 Gray Mar. 25, 1941 2,238,381 Batchelor Apr. 15, 1941 2,327,222 Sell Aug. 17, 1943 2,342,245 Bruce Feb. 22, 1944 2,412,822 Malter Dec. 17, 1946 

